The following abbreviations are herewith defined:
3GPPthird generation partnership projectATallocation tableC_RNTIcell radio network temporary identifierDLdownlink (node B to UE)FECCforward error correction codeHOhand overHShigh speedHSDPAhigh speed data packet accessL1layer 1, physical (PHY) layerLTElong term evolutionMCSmodulation coding schemeNode Bbase stationOFDMorthogonal frequency division multiplexPSKphase shift keyingPTCCHpacket timing advance control channelQAMquadrature amplitude modulationRLIDradio link identifierRNCradio network controlRRCradio resource controlSCCHshared control channelSFRsoft frequency reuseSTBCspace-time block codingTAtiming advanceUEuser equipmentULuplink (UE to Node B)UMTSuniversal mobile telecommunications systemUTRANUMTS terrestrial radio access networkE-UTRANevolved UTRAN, also referred to asUTRAN-LTE and as 3.9GWCDMAwideband code division multiple access
Embodiments of a unified entry format for common control signaling are described in commonly owned U.S. patent application Ser. No. 11/509,697 and entitled “UNIFIED ENTRY FORMAT FOR COMMON CONTROL SIGNALLING”, which is incorporated by reference herein in its entirety. This commonly owned patent application relates to resource allocation for beyond 3G systems, E-UTRA air interface technology, and more particularly to the structure of an Allocation Table (AT), also known as a shared signaling channel, shared control channel (SCCH) or similar. The AT provides a means delivering SCCH information to all UEs within a cell.
In the E-UTRA system the base station (eNodeB) in the network side allocates the radio resources for both DL and UL, and indicates the allocations to the UE on the downlink SCCH. The SCCH carries other information common to all receiving UEs such as, but not limited to, paging indicators and Random Access response. Additional information, such as acknowledgements of the previously transmitted uplink packets for UL traffic and transport formats for the allocated resources, is also present on the SCCH.
The resource allocation entry for a given UE has a predefined structure (unified entry format). However, the number of UEs that are allocated resources in the DL and the UL can vary from sub-frame to sub-frame, and thus the number of entries in the resource AT may not be constant. Consequently, the amount of control signaling transmitted in any given sub-frame in the downlink can differ from sub-frame to sub-frame.
The use of HSDPA HS-SCCH, i.e., UE-specific control signaling, would introduce undesirable overhead due to tail bits from the encoding blocks and bit-field reservations for ACK/NACK signaling. In E-UTRA, contrary to the HSDPA, UL resource allocations are also transmitted in the DL SCCH. Additionally, other UL allocation related control information, such as Power Control and Timing Advance, may be transmitted in the DL SCCH. Further, there are certain specific bit-fields that may be present, such as Paging indicators, which are shared by two or more UEs, and Random Access response, which are shared among random UEs attempting random access to the network. Thus, the use of a UE-specific signaling scheme is not desirable. On the contrary, it is favorable from the overhead and processing point of view to signal to several UEs in the same block and to jointly encode the control signals of multiple UEs respectively.
In joint encoding of the downlink shared control signal, multiple instances of control data (signaling bit-fields) are combined into a single block that is encoded with a FECC. However, as the encoded block length of the control signaling field is dependent on multiple sources of control data, the length of the field can be variable as was noted above, and a UE that is decoding the SCCH requires knowledge of the length of the encoded block. One possibility is to decode blindly, but the number of possibilities is so large that this scheme would not be feasible. Alternatively, the UE could be informed of the length of the encoded field by higher layer signaling. However, it can be shown that this approach would be too slow and inflexible for L1 signaling purposes. Such a scheme would actually limit the performance and increase the latency of the L1 processing.
Uniform encoding and modulation of the DL SCCH provides the lowest encoding overhead, but it exhibits certain drawbacks. As all the UEs in the cell area must be able to detect and decode the SCCH, the channel coding rate needs to be defined for the most difficult reception conditions, and the coding rate is required to be sufficiently low to provide for adequate decoding quality, even at the cell edge. In practice, the encoding rate may need to be set so low that the SCCH overhead of the total DL capacity becomes unsustainable.